What I've done many times when I didn't have enough money, I made peanut butter and jelly sandwiches.
$20 can buy four loaves of bread @ $2.00 each, two jars of peanut butter @ 2/$5.00 and two jars of jelly at about $3.00 each.That's $19.00, so I have some change left over in case they put a tax on the jelly.